The FX818 is an innovative CTCSS Codec designed for the latest generation of Land Mobile Radio equipment. The FX818 is full duplex and has many advanced features which assist the operation of modern CTCSS based systems. The FX818 is electrically, physically and software compatible with the FX828. It permits manufacturers to add new features to their equipment with minimal design changes. The FX818 incorporates a programmable tone decoder which can be set to respond to between 1 and 15 CTCSS tones with minimum software intervention. In addition, a 'Fast' CTCSS detector can respond to a single programmed tone in 60ms, or can be used to provide an output if any CTCSS tone is present at the detector input. A high resolution tone encoder performs accurate generation of any CTCSS tone in current use. High pass and low pass filters are included to provide filtering for CTCSS and Voice band signals. On chip audio summation amplifier and digital adjustable modulator drivers ensure easy integration into equipment. The FX818 along with the FX828 is offered in a choice of small SSOP and SOIC 24-pin packages. It may be used with 3.0 to 5.5 volt supply.